An organic electroluminescence element (i.e., a so-called organic EL element) using electroluminescence (referred to as EL hereinafter) of an organic material is a thin-film type completely-solid element capable of emitting light at a low voltage of several volts to several tens volts, and has many excellent features such as high brightness, high luminous efficiency, thin in thickness, light in weight and the like. Therefore, recently the organic electroluminescence element has attracted attention as a backlight for various kinds of displays, a display board (such as a signboard, an emergency light or the like), and a planar light-emitting body such as a light source for a lighting fixture.
Such an organic electroluminescence element is configured by two layers of electrodes, and a light emitting layer formed of an organic material sandwiched between the two layers of electrodes; and the light emitted by the light emitting layer is transmitted through the electrode(s) and extracted to the outside. Thus, at least one of the two layers of electrodes is configured as a transparent electrode.
Generally, the transparent electrode is formed by an oxide semiconductor material, such as indium tin oxide (SnO2—In2O3) or the like; however, there is also a proposal in which the transparent electrode is formed by laminating ITO and silver to reduce resistance (see, for example, Patent Documents 1 and 2). However, since ITO contains indium, which is a rare metal, the material cost goes up; and further, in order to reduce resistance, it is necessary to perform an annealing treatment at about 300° C. after film-formation. To solve such problem, there is proposal in which the transparent electrode has a configuration in which a metal material with high electrical conductivity, such as silver, is formed into a thin-film, or a configuration in which aluminum is mixed into silver to thereby form a film having a film-thickness less than that formed by silver only to ensure electrical conductivity (see, for example, Patent Document 3).